1. Field of the Invention
This invention relates generally to computer hardware and, more particularly, to a method and apparatus for isolating faulty semiconductor devices in a multiple stream graphics system.
2. Description of the Related Art
In modem video graphics systems, streams of digital bits have taken the place of the traditional reel of celluloid film composed of individual still photographs. The laborious task of processing video data may now be done with the assistance of processors in the video graphics systems, which may be capable of working on multiple streams of data from a variety of sources at once. For example, a single video graphics system may receive streams of data from devices such as a digital camera, a graphics rendering device, a computer-assisted design program, and the like. The video graphics system may also provide post-processed video data to a variety of output devices, including video projectors, televisions, monitors, and the like.
Video graphics systems may include tens or hundreds of semiconductor devices designed to perform various functions. Like all complex semiconductor devices, the semiconductor devices in the video graphics system may occasionally have intrinsic defects that cause the video graphics system to operate in an undesirable manner. The semiconductor devices may also become faulty during operation of the video graphics system. Even a single faulty semiconductor device can cause the video graphics system to operate in an incorrect or undesirable manner, so it is desirable to isolate faults to a single failing semiconductor device.
However, the increasing complexity of video graphics systems, and corresponding decreasing size of their semiconductor elements, has made it increasingly difficult to test the video graphics system. Simply observing the screen output of the video graphics system may reveal undesirable operation, but it may not be a sensitive enough test to detect some errors in high resolution video outputs. Nor may observing the screen provide any indication of which semiconductor device may be faulty. External test equipment like logic analyzers, logic probes and/or oscilloscopes may also have limited usefulness as the size of the semiconductor components continues to decrease.
In recent years, signature analysis using signature registers included in the video graphics system has been developed to provide reliable indications of the correct operation of digital systems. However, trying to isolate faults down to a single component level using signature registers is difficult when there are, for example, 92 semiconductor devices involved in the video graphics system where no signature registers can be put into 64 of the semiconductor devices.
The problems are exacerbated when more than one video stream is provided to the video graphics system. Data from the multiple video streams generally travels through the same data path in the video graphics system, but the data streams may be asynchronous. For example, depending on the particular processing operations, processing of one frame from one data stream may finish while the processing of another frame may only be halfway done. The order in which bits from the multiple video streams may be processed may also not be deterministic. Signature registers typically only work when signature analyzing deterministic data from one video stream or synchronous data from multiple video streams.